1. Field of the Invention
The present invention generally relates to a width adjusting device for a paper web, which adjusts the width of the paper web for a printing system prior to a printing section. More particularly, the present invention relates to a lithographic rotary press which is equipped with at least one of the width adjusting device and a plurality of printing sections through which the paper web is successively travelled to be printed.
2. Description of the Prior Art
A typical conventional lithographic rotary press adapted for a color printing system is, for example shown in FIG. 4 which is a schematically elevational view. This conventional lithographic printing system comprises a plurality of printing sections P each of which includes two pairs of a combination of a plate cylinder PC and a blanket cylinder BC. The blanket cylinders BC of each the printing section P are vertically arranged to be in contact with each other. In this conventional printing system, four sets of the printing sections P are horizontally arranged in parallel as shown in FIG. 4. A paper web W is also horizontally travelled through the printing sections in which the paper web W is successively passed between the pairs of the blanket cylinders BC, BC to print both sides of the paper web W.
Another conventional lithographic rotary press for a color printing system is shown in FIG. 5. In this drawing, four printing sets each of which is composed of a plate cylinder PC and a blanket cylinder BC are radially arranged about an impression cylinder IC as a common center cylinder. The blanket cylinders BC are respectively in contact with the impression cylinder IC to form printing sections P. A paper web W is roundly travelled along the circumference of the impression cylinder IC so that the paper web W is successively passed through the four printing sections P defined between the blanket cylinders BC and the impression cylinder IC to print one side of the paper web W.
In recent years, many newspaper publishers have progressed to print newspaper in color inks and thus demanded to perform such color printing on many pages at a high speed in a limited printing space.
In order to satisfy such demands, another conventional lithographic rotary press for a color printing system has been proposed as shown in FIG. 6. In this printing system, each printing section P includes two sets of a blanket cylinder BC and a plate cylinder PC which are symmetrically arranged so as to bring the blanket cylinders BC into contact with each other. A paper web W is vertically travelled through the four printing sections P to print both sides of the paper web W in the same manner as the above described systems. This type of printing system is for example shown in "IFRA Newspaper Techniques English Edition", pp.64 to pp.73; April, 1988 published by INCA-FIEJ Research Association.
Paper webs used in various printing systems are generally produced in such manner that pulp fibers are mechanically cut and broken into fine particles; dispersed in water; dehydrated and dried; and finally adhered by hydrogen-bond to form paper in a web or sheet figure. Under moisture conditions, each of pulp fibers tends to extend a little less than 1 percent in its longitudinal direction and 20 to 30 percent in its radius direction. Thus, the paper web is extended in its longitudinal and width directions by dampening and/or watering operation. Most of the pulp fibers of general mechanically produced paper webs are orientated in the longitudinal direction of the paper web, so that paper webs are remarkably extended in their width direction.
In a specific lithographic printing system employing dampening or watering operation in printing a section, a paper web is swelled by the water supplied during the dampening operation. Therefore the image and lines printed on the paper web are also deformed in response to the swell of the paper web. In the printing systems including at least two lithographic printing sections each of which is associated with dampening means to successively print color images on the same paper web, the printed images or lines formed at the first printing section are not correctly coincided with the images or lines formed at the second and later printing sections. Accordingly, this will produce printed materials with poor quality.